1. Field of the Invention
The present invention relates to a spindle protective structure in a spindle-through coolant feeder.
2. Description of Related Art
As a spindle structure used in a high-speed rotating machine tool such as a drilling machine and a tapping machine, or a machining center, there is known a spindle-through coolant feeder for flowing machining fluid for cooling and removing dust though an axial center of a spindle.
FIGS. 5 and 6 are schematic sectional views of conventional spindle structures using spindle-through coolant.
In the spindle structure of FIG. 6, an axial through hole 2 is bored through a spindle 1 and a pipe 4 is connected to an end of the spindle 1 through a rotary joint 3 so that coolant from the pipe 4 is led through the rotary joint 3 and the though hole 2 to a tip of a tool 5. A drain pipe 6 is provided at the rotary joint 3 in order to discharge coolant overflowing in the rotary joint 3 to the outside.
Such structure is not free from problems such as power loss and oscillation of the spindle 1, since the spindle 1 is driven by an induction motor 8 through a gear train 7, a belt or the like. Therefore, it is not necessarily suitable for real high-speed rotation.
In order to solve the above problems, a spindle structure shown in FIG. 5 has been proposed. In this structure, in addition to a though hole 2 bored through a spindle 1, an axial through hole 10 is bored through a rotor shaft of an induction motor 8. The spindle 1 and the rotor shaft 9 are coupled by a coupler 11, and coolant from a pipe 4 is led through a rotary joint 3 which is fitted to a rotary joint support housing 12 provided at an end of the induction motor 8 and then through the through hole 10 and the through hole 2 to a tip of a tool 5. Since the spindle 1 is driven by the induction motor 5 directly, the structure is free from problems such as power loss and oscillation of the spindle 1, and suitable for real high-speed rotation. A drain pipe 6 is provided at the rotary joint support housing 12 in order to discharge coolant overflowing in the rotary joint 3 to the outside.
In recent spindle-through coolant feeders, coolant of high pressure such as 70 atm. is generally used in order to raise the efficiency of discharging dust and cooling a knife edge of a tool 5 and to improve a finished state of a workpiece. Therefore, if a flaw is made at a rotary joint 3, there is a risk that a large amount of coolant may leak out in a moment. In the case of the structure of FIG. 6, coolant may reach the periphery of the spindle 1, and in the case of the structure of FIG. 5, coolant may flow directly inside the induction motor 8. In either case, it may cause serious problems such as rust, abnormal rotation, or electrical failure. Further, if coolant is not fed to the tip of a tool 5 normally, the tool 5 or a workpiece may be damaged.
Conventionally, flow control of coolant is performed checking the flow of coolant jetting from the tip of a tool 5 by visual observation, or performed depending on a flow sensor provided in the line of a pipe 4 for feeding coolant. In such conventional flow control, leakage of coolant around a rotary joint 3 cannot be detected directly, so that it takes time for an operator to deal with the leakage. Therefore, the conventional flow control is not enough to solve the above mentioned problems related to recent use of high pressure coolant.